Theoretical designs have been carried out which demonstrate the possible weight and volume reductions to be obtained when using amorphous metal in place of silicon-iron for the core material in medium frequency power transformers. The amorphous metal provides such savings by its ability to operate at high flux densities without excessive core losses. The reduced core size also benefits the winding size, the overall reduction in weight and volume is particularly appropriate for rail and air borne power supply equipment. Of the various amorphous metal alloys available in ribbon form, two were selected for evaluation for the frequency band 50 to 3000 Hz. Several cores were built suitable for use in a3 kHz 20 kVA transformer using purpose built core winding facilities. The wound cores, after annealing, were subjected to a comprehensive series of tests using both sinusoidal and square wave supply voltages. The thesis contains a valuable analysis of the results obtained and related to the magnetic properties of amorphous metal. The effect of mechanical stresses has also been investigated. The wound amorphous ribbon cores were found to be slightly flexible and prone to flaking, as a consequence several methods of core protection were investigated. Temperature rise tests have been conducted on the completed cores and various methods of heat dissipation tried. The research has shown the viability of the use of amorphous metal for the cores of medium frequency power transformers.